Tag: botany

In a fully developed male gametophyte, three nuclei are present i.e., one vegetative nucleus and two male nuclei.

A typical carpel consists of ovary which can have many ovules. Each ovule has an embryo sac, which in turn has a single egg cell. Similarly, in majority of angiosperms each stamen consists of a bilobed anther, which in turn has two pollen sacs in each lobe, consisting of pollen grains.

A pollen tube is a tubular structure produced by the male gametophyte of seed plants when it germinates. They act as conduits to transport the male gamete cells from the pollen grain—either from the stigma (in flowering plants) to the ovules at the base of the pistil or directly through ovule tissue in some gymnosperms. Pollen tube formation is important for sexual reproduction to occur in seed plants. Pollen tubes are unique to plants and their structure had evolved over plant history.

Polyspermy refers to a situation where more than two sperms are released in an embryo sac. This may result because of the formation of more than two sperms in a pollen tube or due to the penetration of an embryo sac by more than one pollen tube. In angiosperms, the pollen tube is normally an unbranched structure which collapses soon after fertilization, the pollen tube may persist for as long as three weeks. Intine is the inner, more or less uniform, pectocellulosic layer of pollen grain wall, which is destroyed during acetolysis. Morphologically, the exine is divisible into two distinct layers: (i) an outer sculptured layer called sexine, and (ii) an inner non-sculptured layer, nexine. The sexine further comprises an internal layer of upright rod-like elements, the columellae(bacula) covered over by a roof-like layer, the tectum. The exine is, thus, typically33-layered consisting of tectum, columella, and nexine. The tectum may be smooth or have various types of processes.

Pollen is a fine to coarse powdery substance comprising pollen grains which are male microgametophytes of seed plants, which produce male gametes (sperm cells). The study of pollen is called palynology and is highly useful in paleoecology, paleontology, archaeology, and forensics.

Each pollen grain is a minute body, of varying shape and structure, formed in the male structures of seed-bearing plants and transported by various means (wind, water, insects, etc.) to the female structures, where fertilization occurs. In angiosperms, pollen is produced by the anthers of the stamens in flowers.

Ubisch bodies found in tapetal cells help in pollen formation by participating in the external thickening of exine. They occur during spore wall formation and migrate to the cell cavity, where they are coated with sporopollenin and are released into the anther cavity. 

Staminode is the term used for the sterile stamen that does not make the pollen grain and appears like petals, as seen in Canna. 

The pollen exine of the pollen grains consists most resistant biological material known as Sporopollenin. It is resistant to both microbial and chemical decomposition by which it preserves pollen grains during fossilization.